I interviewed at a place that managed traffic light behavior and they had a system to evaluate traffic efficiency by watching traffic flow through the whole area, tracked using ambient Bluetooth signals from phones.
What does this mean? Are they just measuring radio power levels in the 2.4GHz spectrum, and using that to determine whether a car is there or not? Or are they actually somehow capturing bluetooth signals, decoding them, and extracting identifiers (eg. MAC) from them?